Communication device, communication system, and method of allocating bandwidth

ABSTRACT

A communication device operating as a master unit includes: a MAC layer termination functioning unit for extracting, from a receiving signal, queue length information scheduled to be transmitted from an ONU, and controlling transmission of a grant to the ONU; a traffic monitor for measuring an amount of uplink traffic of each ONU; and a bandwidth allocation functioning unit for determining a bandwidth to be allocated to each ONU based on the queue length information extracted by the MAC layer termination functioning unit, the amount of traffic measured by the traffic monitor, and a bandwidth that can be allocated in one cycle of bandwidth update, and issuing a grant according to the determination. The bandwidth allocation functioning unit updates a bandwidth to be allocated periodically.

TECHNICAL FIELD

The present invention relates to a method of allocating a bandwidth in apoint-to-multipoint communication system.

BACKGROUND ART

In a point-to-multipoint communication system such as a PON (PassiveOptical Network) system conventionally employed, an OLT (Optical LineTerminal) periodically updates an amount of bandwidth allocation whichis information on a transmission grant that is to be given to an ONUs(Optical Network Unit). For efficient use of a bandwidth, the OLTdetermines an amount of bandwidth allocation according to the trafficcondition of the ONUs. When transmitting variable-length data such asEthernet frames (registered trademark) in the PON system, for example,the length of a grant designated by the OLT and a delimitation of datatransmitted from the ONUs may not be at the same point. This generates atime period not used for uplink data transmission, resulting in a lossof a bandwidth. In this regard, in the conventional PON system, the ONUsends a report message to notify a queue length corresponding to theamount of data accumulated in an uplink buffer according to adelimitation in variable-length data. Then, the OLT allocates a grantcorresponding to the queue length. In this manner, the OLT can fully usethe allocated grant for data transmission, so that the OLT achievesbandwidth allocation without loss (see Patent Literature 1 andNon-Patent Literature 1 cited below).

Patent Literature 1: Japanese Patent Application Laid-open No.H11-146000

Non-Patent Literature 1: “Dynamic Bandwidth Allocation Algorithm forGE-PON” by YOSHIHARA et al., technical report NS2002-17 of the Instituteof Electronics, Information and Communication Engineers

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

According to the aforementioned conventional technique, a queue lengthis notified in accordance with to the amount of uplink data accumulatedin an uplink buffer. Accordingly, there has been a problem that the OLTcan allocate a grant only after uplink data is accumulated in a bufferof the ONU, resulting in a delay in uplink data transmission. To bespecific, not only a time required for propagation through an opticalsubscriber line, but also a time corresponding to one cycle of bandwidthupdate required for accumulation of data in an uplink buffer of the ONUshould be considered.

Specifically, throughput relies on the round-trip time of data and thelike especially if a user application employs a communication protocolsuch as TCP/IP according to which next data is transmitted after aresponse from an opposite terminal is received. Accordingly, a delaytime should be reduced to obtain a high throughput.

In the conventional PON system, the limiting value of a transmissionspeed within a PON section is lower than the limiting value ofthroughput, so that a delay time does not present any problems. If thepropagation time of an optical signal within a PON communication path of20 km is 0.2 ms, for example, one cycle of bandwidth update is about 0.3ms that is a shortest period determined in consideration of a timerequired for bandwidth calculation. In this case, the round-trip time is0.5 ms that is the total of the propagation time and one cycle ofbandwidth update. Accordingly, the highest throughput provided by theconventional technique is 1 Gbps, and it does not exceed the limit ofthe transmission speed in a PON section. As a result, a delay caused byaccumulation of data in the ONU will not come to the surface if thetransmission speed in a PON section does not exceed 1 Gbps.

However, a delay time becomes a bottleneck if the transmission speed ina PON section is increased. To be specific, TCP/IP throughput remains as1 Gbps as long as the conventional bandwidth allocation system isemployed even if the transmission speed in a PON section is increased to10 Gbps, for example. Accordingly, there has been a problem that inorder for four terminals to make concurrent transmission, for example,only a bandwidth of about 4 Gbps can be used even if a room is left in aPON bandwidth, resulting in low efficiency of use of a bandwidth. Also,in this case, an end user cannot enjoy a benefit gained by upgrading.

The present invention has been made in view of the foregoing. It is anobject of the invention to provide a method of allocating a bandwidthcapable of increasing throughput by reducing a waiting time in uplinktransmission by a terminal device.

Means for Solving Problem

In order to solve the aforementioned problems, a communication deviceoperating as a master unit in a point-to-multipoint communication systemin which the master unit and slave units transmit and receive variablelength data to and from each other according to one aspect of thepresent invention is constructed in such a manner as to include: MAClayer termination functioning unit configured to control an extraction,from an incoming signal, of queue length information scheduled to betransmitted from the slave units, and a transmission of a grant to theslave units; traffic monitoring unit configured to measure an uplinktraffic amount of each of the slave units; and bandwidth allocationfunctioning unit configured to determine a bandwidth to be allocated tothe slave units based on the queue length information extracted by theMAC layer termination functioning unit, the traffic amount measured bythe traffic monitoring unit, and a bandwidth that can be allocated inone cycle of bandwidth update, and issue a grant in accordance with thedetermination, wherein the bandwidth allocation functioning unitperiodically updates a bandwidth to be allocated.

EFFECT OF THE INVENTION

The method of allocating a bandwidth according to the present inventioncan reduce a waiting time in uplink transmission by an ONU.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of the configuration of a PON system in a firstembodiment.

FIG. 2 is a flow chart for explaining a method of calculating abandwidth to be allocated employed in the first embodiment.

FIG. 3 is a timing chart showing bandwidths allocated before and afterupdate of bandwidth allocation when a surplus bandwidth is small.

FIG. 4 is a timing chart showing bandwidths allocated before and afterupdate of bandwidth allocation when a surplus of bandwidth is large.

FIG. 5 shows an example of the configuration of a PON system in a secondembodiment.

FIG. 6 is a flow chart for explaining a method of calculating abandwidth to be allocated employed in the second embodiment.

FIG. 7 is a timing chart showing bandwidths allocated before and afterupdate of bandwidth allocation when the number of terminals to makeconcurrent transmission is large.

FIG. 8 is a timing chart showing bandwidths allocated before and afterupdate of bandwidth allocation when the number of terminals to makeconcurrent transmission is small.

EXPLANATION OF LETTERS AND NUMERALS

1, 1B OLT

2 Splitter

3-1, 3-2, 3-3 ONU

11 Optical transmitter and receiver

12 MAC layer termination functioning unit

13, 13B Bandwidth allocation functioning unit

14 Traffic monitor

15 SNI

100, 101, 102, 103, 104, 105, 200, 201, 202, 300, 301, 302, 303, 304,305, 400, 401, 402, 403, 404, 405, 500, 501, 502, 503, 504, 505, 506,507, 600, 601, 602, 603, 700, 701, 702, 703, 800, 801, 802, 803Bandwidth

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Embodiments of a method of allocating a bandwidth according to thepresent invention will be described in detail below based on drawings.The embodiments are not intended to restrict the invention. In thedescription below, a case in which the method for allocating a bandwidthis applied in a PON system is described as an example.

First Embodiment

FIG. 1 shows an example of the configuration of a PON system in thepresent embodiment. The PON system shown in FIG. 1 includes an OLT 1that is a station unit placed in a station housing of atelecommunications carrier, a splitter 2 that is an optical branchingnetwork including an optical fiber and a power splitter, and ONUs 3-1,3-2 and 3-3 that are subscribers' units placed in subscribers'residences. The OLT 1 includes an optical transmitter and receiver 11, aMAC layer termination functioning unit 12, a bandwidth allocationfunctioning unit 13, and a traffic monitor 14.

The optical transmitter and receiver 11 converts a downlink signal to anoptical signal, and transmits the optical signal to each of the ONUs.The optical transmitter and receiver 11 also converts an uplink opticalsignal received from each of the ONUs to an electrical signal. The MAClayer termination functioning unit 12 extracts queue length reportinformation received from each of the ONUs, and outputs the extractedqueue length report information to the bandwidth allocation functioningunit 13. Further, the MAC layer termination functioning unit 12generates a grant on the basis of grant information notified from thebandwidth allocation functioning unit 13. The MAC layer termination unit12 multiplexes the grant with a downlink signal directed to each of theONUs, and outputs the resultant signal to the optical transmitter andreceiver 11. The bandwidth allocation functioning unit 13 manages grantsto be allocated to the respective ONUs so that uplink signals from theONUs will not collide with each other. The bandwidth allocationfunctioning unit 13 calculates a bandwidth to be allocated to each ofthe ONUs on the basis of the queue length report information notifiedfrom the MAC layer termination unit 12, and the traffic amount notifiedfrom the traffic monitor 14. Then, the bandwidth allocation functioningunit 13 determines grant information (containing a bandwidth to beallocated and an allocation starting time) regarding each of the ONUs onthe basis of the result of the calculation, and notifies the MAC layertermination functioning unit 12 of the grant information. The trafficmonitor 14 monitors the amount of actual data received from each of theONUs, and notifies the bandwidth allocation functioning unit 13 of themonitored amount. An SNI (service network interface) 15 is an interfacethrough which connection is made to a service network (not shown).

The operation of bandwidth allocation of the PON system having theaforementioned configuration will be described next. FIG. 2 is a flowchart for explaining a method of calculating a bandwidth to be allocatedemployed in the first embodiment.

In order to update the amount of grant allocation periodically, thebandwidth allocation functioning unit 13 performs the operation shown inFIG. 2 in each cycle to determine a bandwidth to be allocated in a nextcycle. The bandwidth allocation functioning unit 13 acquires the amountof data actually transmitted from each of the ONUs in a previous cycleon the basis of the amount of actual data notified from the trafficmonitor 14. Then, the bandwidth allocation functioning unit 13 refers toqueue length report information notified from the MAC layer terminationunit 12 and the acquired traffic amount, and calculates a surplusbandwidth on the basis of them (step S1). More specifically, thebandwidth allocation functioning unit 13 determines an amount obtainedby reflecting a queue length and the amount of traffic as a necessarybandwidth for each ONU and subtracts the necessary bandwidth from abandwidth that can be allocated in one cycle of bandwidth update. Asurplus bandwidth may be calculated in various ways according to how thequeue length and the amount of traffic are reflected. Some examples ofthe calculation are given below, although they may be replaced by adifferent method.

First Method of Calculation

A surplus bandwidth is acquired by subtracting the queue length and thetraffic amount of an ONU from a bandwidth that can be allocated in onecycle of bandwidth update. The queue length of an ONU corresponds to theamount of data already accumulated in a buffer of the ONU, anddetermined to be transmitted. The traffic amount corresponds to theamount of data actually received in a previous cycle, namely apreviously executed performance, and indicates a tendency of the amountof transmission data. In this case, a necessary bandwidth defined by anamount of data to be transmitted and the previous performance issubtracted, and the remainder is regarded as being a surplus bandwidth.

Second Method of Calculation

A surplus bandwidth is acquired by subtracting the queue length of anONU from a bandwidth that can be allocated in one cycle of bandwidthupdate. In this case, a necessary bandwidth that is defined by an amountof data determined to be transmitted is subtracted, and the remainder isdefined as a surplus of bandwidth.

Third Method of Calculation

A surplus of bandwidth is acquired by subtracting a receiving trafficfrom an ONU from a bandwidth that can be allocated in one cycle ofbandwidth update. In this case, a necessary bandwidth that is defined bythe previous performance is subtracted, and the remainder is defined asa surplus of bandwidth.

Fourth Method of Calculation

A surplus of bandwidth is acquired by subtracting the queue length of anONU and receiving traffic that is multiplied by a value (coefficient)that is a normalized value of a surplus bandwidth in a previous cyclefrom a bandwidth that can be allocated in one cycle of bandwidth update.In this case, a necessary bandwidth is determined not only by the amountof data scheduled to be transmitted, but also by a value that isobtained by multiplying a value of previous performance by theaforementioned coefficient for reflecting a tendency of the amount oftransmission data. The necessary bandwidth thereby determined issubtracted, and the remainder becomes a surplus of bandwidth.

After a surplus bandwidth is acquired in the aforementioned manners, thebandwidth allocation functioning unit 13 determines a coefficient bywhich the acquired surplus bandwidth is reflected in bandwidthallocation. This coefficient is supposed to be m, for example. Thebandwidth allocation functioning unit 13 determines the coefficient m,for example, by means of the following method (step S2) on the basis ofthe surplus bandwidth acquired in step S1.

In one example, m is set to “1” if the surplus bandwidth is equal to orlarger than a predetermined threshold, and is set to “0” if the surplusbandwidth is smaller than the predetermined threshold. In anotherexample, m is determined by comparing the surplus of bandwidth with abandwidth that can be allocated in one cycle of bandwidth update andnormalizing the surplus bandwidth. These examples may be applied incombination. The coefficient m may be determined by a different method.

After the coefficient m is determined in the foregoing manner, thebandwidth allocation functioning unit 13 calculates a bandwidth to beallocated in the next cycle for each ONU (step S3). More specifically, abandwidth to be allocated in the next cycle is calculated, for example,as follows:

Bandwidth to be allocated in the next cycle=Queue length of anONU+m×(Traffic amount of the ONU)

The bandwidth allocation functioning unit 13 makes this calculation forall ONUs, so as to acquire bandwidths to be allocated in the next cyclefor each of the ONUs.

The bandwidth allocation functioning unit 13 determines grantinformation (step S4) on the basis of the thus obtained bandwidthsthereby acquired to be allocated in the next cycle.

The coefficient m is determined by the aforementioned examples.Accordingly, if there is a large surplus of bandwidth, namely if theamount of uplink data transmitted from an ONU tends to be small, byadding a certain amount of bandwidth based on the traffic amount, dataaccumulated in an ONU buffer after transmission of a queue length reportcan also be transmitted. On the other hand, if a surplus bandwidth issmall, namely if the amount of uplink data transmitted from an ONU tendsto be large, only a bandwidth in an amount based on queue lengthinformation is allocated, and no predicted bandwidth allocation isincluded. By doing so, data already accumulated in an ONU buffer can betransmitted without fail. As described, a bandwidth is allocated inaccordance with the amount of a surplus bandwidth, thereby realizingefficient bandwidth allocation.

The aforementioned calculation of the coefficient may be made for eachcycle of bandwidth update, or for a given cycle. If the coefficient iscalculated for a given cycle, a bandwidth to be allocated is determinedon the basis of the latest coefficient.

A status of bandwidths in the PON system allocated by employing theforegoing method of bandwidth allocation will be described next. In theexamples given below, m is set to zero and the traffic amount is notused for allocation if a surplus of bandwidth is smaller than apredetermined threshold. On the other hand, m is made the aforementionednormalized value if a surplus bandwidth is equal to or larger than thepredetermined threshold.

FIG. 3 is a timing chart showing bandwidths allocated before and afterthe update of bandwidth allocation when a surplus bandwidth is small.The ONUs 3-1, 3-2 and 3-3 in the PON system shown in FIG. 1 transmitdata #1 (hereinafter called D#1), D#2 and D#3 respectively to the OLT 1before the update of bandwidth allocation. At this time, bandwidths 100and 200 are allocated to the ONU 3-1. Likewise, bandwidths 101 and 201are allocated to the ONU 3-2, and bandwidths 102 and 202 are allocatedto the ONU 3-3. The bandwidths allocated to the respective ONUs includethe bandwidths 100 to 102 based on queue lengths, and the bandwidths 200to 202 based on receiving traffic.

For bandwidth update, the OLT 1 determines bandwidths to be allocated ina new cycle of bandwidth update in the manner described above. Here, itis shown a case where the OLT 1 determines that a surplus of bandwidthis small. In this case, the OLT 1 allocates a bandwidth based only on aqueue length, and does not allocate a bandwidth based on the amount oftraffic. As a result, after the update of bandwidth allocation, the ONUs3-1, 3-2 and 3-3 transmit data D#11, D#12 and D#13 in bandwidths 103,104 and 105, respectively. The allocated bandwidths 103 to 105 arebandwidths based on queue lengths.

FIG. 4 is a timing chart showing bandwidths allocated before and afterupdate of bandwidth allocation when a surplus bandwidth is large. TheONUs 3-1, 3-2 and 3-3 in the PON system shown in FIG. 1 transmit data#21 (hereafter called D#21), D#22 and D#23 respectively to the OLT 1before the update of bandwidth allocation. At this time, bandwidths 300and 400 are allocated to the ONU 3-1. Likewise, bandwidths 301 and 401are allocated to the ONU 3-2, and bandwidths 302 and 402 are allocatedto the ONU 3-3. The bandwidths allocated to the ONUs include thebandwidths 300 to 302 based on queue lengths, and the bandwidths 400 to402 based on receiving traffic.

Here, it is shown a case where the OLT 1 determines that a surplusbandwidth is large. In this case, in addition to a bandwidth based on aqueue length as described above the OLT 1 additionally allocates abandwidth based on the amount of traffic. As a result, after the updateof bandwidth allocation, the ONU 3-1 transmits data D#31 usingbandwidths 303 and 403, the ONU 3-2 transmits data D#32 using bandwidths304 and 404, and the ONU 3-3 transmits data D#33 using bandwidths 305and 405. The allocated bandwidths 303 to 305 are bandwidths based onqueue lengths, and the allocated bandwidths 403 to 405 are bandwidthsbased on the amounts of traffic.

As described above, in the present embodiment, not only the amount ofdata scheduled for transmission that is based on a queue length report,but the amount of data expected to be transmitted that is based on theamount of traffic is also evaluated to determine a bandwidth to beallocated. Thus, data accumulated in an ONU buffer during an RTT (RoundTrip Time) can also be transmitted when a bandwidth is granted. Thisrealizes reduction of data accumulated in the ONU buffer, leading to areduction in waiting time for uplink transmission by the ONU. Since asurplus bandwidth is calculated for each cycle of bandwidth update, abandwidth to be allocated can be changed in accordance with the state ofutilization of a bandwidth within a PON communication path. As a result,an end user can be given high throughput at an application level.

In the present embodiment, the amount of traffic is multiplied by avalue (coefficient) proportionate to a surplus bandwidth. However, aqueue length may also be multiplied by the same coefficient. In thiscase, a bandwidth to be allocated may be derived by the above samemethod. Alternatively, these methods may be employed in combination.

Further, in the present embodiment, the method of bandwidth allocationof the invention is applied to a PON system. The method of bandwidthallocation of the invention may also be applied to a differentcommunication system other than a point-to-multipoint communicationsystem. The OLT and the ONUs in the present embodiment operate as amaster unit and slave units, respectively, and the similar structuresand the operations thereof are also applicable to the differentcommunication system.

Second Embodiment

In the first embodiment, for carrying out a dynamic bandwidthallocation, a surplus bandwidth is used as a parameter, and queue lengthinformation and the amount of traffic are reflected to a bandwidth to beallocated. In the present embodiment, a case in which the number of ONUsto make concurrent transmission is used as a parameter is explained.

FIG. 5 shows an example of the configuration of a PON system in thesecond embodiment. As seen from the comparison with the PON system shownin FIG. 1, the PON system shown in FIG. 5 includes an OLT 1B instead ofthe OLT 1, and the OLT 1B includes a bandwidth allocation functioningunit 13B instead of the bandwidth allocation functioning unit 13 in theOLT 1. The bandwidth allocation functioning unit 13B has the samefunction as that of the bandwidth allocation functioning unit 13, but itcalculates a bandwidth to be allocated in a method (described later)different from that employed by the bandwidth allocation functioningunit 13.

The operation of bandwidth allocation in the PON system having theaforementioned configuration will be described next. FIG. 6 is a flowchart for explaining a method of calculating a bandwidth to be allocatedemployed in the present embodiment.

In order to update the amount of grant allocation periodically, thebandwidth allocation functioning unit 13B performs the operation shownin FIG. 6 in each cycle to determine a bandwidth to be allocated in thenext cycle. The bandwidth allocation functioning unit 13B grasps thequeue length information and the traffic amount of each ONU as describedabove. First, based on grant information managed by the bandwidthallocation functioning unit 13B itself or the like information, thebandwidth allocation functioning unit 13B acquires the number of ONUs(the number of terminals to make concurrent transmission) havingrequested data transmission in the next cycle (step S11). Next, thebandwidth allocation functioning unit 13B determines a coefficient bywhich the thus acquired number of terminals to make concurrenttransmission is reflected in bandwidth allocation. This coefficient issupposed to be n, for example. The bandwidth allocation functioning unit13B determines the coefficient n, for example, by means of the followingmethod (step S12) on the basis of the number of ONUs acquired in stepS11.

In one example, n is set to “0” if the number of terminals to makeconcurrent transmission is equal to or larger than a predeterminedthreshold, and is set to “1” if the number of terminals to makeconcurrent transmission is smaller than the predetermined threshold. Inanother example, the reciprocal of the number of terminals to makeconcurrent transmission is employed as n. These examples may be appliedin combination. The coefficient n may be determined by means of adifferent method.

After the coefficient n is determined in the foregoing manner, thebandwidth allocation functioning unit 13B calculates a bandwidth to beallocated in the next cycle for each ONU (step S13). More specifically,a bandwidth to be allocated in the next cycle is calculated, forexample, as follows:

Bandwidth to be allocated in the next cycle=Queue length of anONU+n×(Traffic amount of the ONU)

The bandwidth allocation functioning unit 13B performs this calculationfor all ONUs, so as to acquire bandwidths to be allocated in the nextcycle for each of the ONUs.

The bandwidth allocation functioning unit 13B determines grantinformation (step S4) on the basis of the thus obtained bandwidths to beallocated in the next cycle.

The coefficient n is set as in the aforementioned example. Accordingly,if the number of terminals to make concurrent transmission is small, inother words, if more bandwidth to be used is available, by adding acertain amount of bandwidth based on the traffic amount, dataaccumulated in an ONU buffer after transmission of a queue length reportcan also be transmitted. On the other hand, if the number of terminalsto make concurrent transmission is large, in other words, if there islittle room left in a bandwidth, only a bandwidth in an amount based onqueue length information is allocated, and no predicted bandwidthallocation is included. By doing so, data already accumulated in an ONUbuffer can be transmitted without fail. As described, a bandwidth isallocated in accordance with the number of terminals to make concurrenttransmission, thereby realizing an efficient bandwidth allocation.

A status of bandwidths in the PON system allocated by employing theforegoing method of allocating a bandwidth will be described next. Inone example given below, the coefficient n is determined on the basis ofwhether the number of terminals to make concurrent transmission is equalto or larger than a predetermined threshold.

FIG. 7 is a timing chart showing bandwidths allocated before and afterthe update of bandwidth allocation when the number of terminals to makeconcurrent transmission is large. The ONUs 3-1, 3-2, 3-3, and 3-4 (ONU3-4 is not shown in FIG. 5) in the PON system shown in FIG. 5 transmitdata #41 (hereafter called D#41), D#42, D#43 and D#44 respectively tothe OLT 1B before the update of bandwidth allocation. At this time,bandwidths 500 and 600 are allocated to the ONU 3-1. Likewise,bandwidths 501 and 601 are allocated to the ONU 3-2, bandwidths 502 and602 are allocated to the ONU 3-3, and bandwidths 503 and 603 areallocated to the ONU 3-4. The bandwidths allocated to the ONUs includethe bandwidths 500 to 503 based on queue lengths, and the bandwidths 600to 603 based on receiving traffic.

For bandwidth update, the OLT 1B determines bandwidths to be allocatedin a new cycle of bandwidth update in the way described above. Here, itis shown a case where the OLT 1B determines that the number of terminalsto make concurrent transmission is equal to or larger than thepredetermined threshold. In this case, the OLT 1B allocates a bandwidthbased only on a queue length, and does not allocate a bandwidth based onthe amount of traffic. As a result, after the update of bandwidthallocation, the ONUs 3-1, 3-2, 3-3 and 3-4 transmit data D#51, D#52,D#53 and D#54 using bandwidths 504, 505, 506 and 507, respectively. Theallocated bandwidths 504 to 507 are bandwidths based on queue lengths.

FIG. 8 is a timing chart showing bandwidths allocated before and afterupdate of bandwidth allocation when the number of terminals to makeconcurrent transmission is small. The ONUs 3-1 and 3-2 in the PON systemshown in FIG. 5 transmit data #61 (hereafter called D#61) or D#62respectively to the OLT 1B before the update of bandwidth allocation. Atthis time, bandwidths 700 and 800 are allocated to the ONU 3-1.Likewise, bandwidths 701 and 801 are allocated to the ONU 3-2. Thebandwidths allocated to the respective ONUs include the bandwidths 700and 701 based on queue lengths, and the bandwidths 800 and 801 based onreceiving traffic.

Here, it is shown a case where the OLT 1B determines that the number ofterminals to make concurrent transmission is smaller than thepredetermined threshold. In this case, in addition to a bandwidth basedon a queue length as described above the OLT 1B additionally allocates abandwidth based on the amount of traffic. As a result, after the updateof bandwidth allocation, the ONU 3-1 transmits data D#71 usingbandwidths 702 and 802. Likewise, the ONU 3-2 transmits data D#72 usingbandwidths 703 and 803. The allocated bandwidths 702 and 703 arebandwidths based on queue lengths, and the allocated bandwidths 802 and803 are bandwidths based on the amounts of traffic.

In the description given above, it is explained that the amount oftraffic is multiplied by a value (coefficient) proportionate to thenumber of terminals to make concurrent transmission. However, a queuelength may also be multiplied by the same coefficient. In this case, abandwidth to be allocated may be derived by the same method as describedabove. These methods may be employed in combination.

In the present embodiment, it is shown a case in which theaforementioned coefficient is determined on the basis of the number ofterminals to make concurrent transmission. However, the number of activeterminals may be employed as the coefficient. However, the bandwidthallocation functioning unit 13B stores the number of active terminalsthat is the number of ONUs registered with the OLT 1B, and determinesthe coefficient on the basis of the number of active terminals stored.The operation of the bandwidth allocation functioning unit 13B is thesame as that described above.

As described above, in the present embodiment, not only the amount ofdata scheduled for transmission that is based on a queue length report,but the amount of data expected to be transmitted that is based on theamount of traffic is also evaluated to determine a bandwidth to beallocated. Thus, data accumulated in an ONU buffer during an RTT canalso be transmitted when a bandwidth is granted. This realizes reductionof data accumulated in the ONU buffer, leading to a reduction in waitingtime for uplink transmission by the ONU. The number of terminals to makeconcurrent transmission is evaluated for each cycle of bandwidth update,a bandwidth to be allocated can be changed in accordance with theutilization state of a bandwidth in a PON section. As a result, an enduser can be given high throughput at an application level.

INDUSTRIAL APPLICABILITY

As described above, the method of allocating a bandwidth according tothe present invention is useful in a point-to-multipoint communicationsystem such as a PON system, and in particular, it is employed suitablyto realize efficient bandwidth allocation.

1. A communication device operating as a master unit in apoint-to-multipoint communication system in which the master unit andslave units transmit and receive variable length data to and from eachother, the communication device comprising: MAC layer terminationfunctioning unit configured to control an extraction, from an incomingsignal, of queue length information scheduled to be transmitted from theslave units, and a transmission of a grant to the slave units; trafficmonitoring unit configured to measure an uplink traffic amount of eachof the slave units; and bandwidth allocation functioning unit configuredto determine a bandwidth to be allocated to the slave units based on thequeue length information extracted by the MAC layer terminationfunctioning unit, the traffic amount measured by the traffic monitoringunit, and a bandwidth that can be allocated in one cycle of bandwidthupdate, and issue a grant in accordance with the determination, whereinthe bandwidth allocation functioning unit periodically updates abandwidth to be allocated, calculates a necessary bandwidth for theslave units on the basis of the queue length information and the trafficamount, and calculates a surplus bandwidth by subtracting the necessarybandwidth from the bandwidth that can be allocated in one cycle ofbandwidth update, determines a coefficient by which the surplusbandwidth is reflected in bandwidth allocation on the basis of the queuelength information and the amount of traffic, and determines a bandwidthto be allocated to the slave units on the basis of the queue lengthinformation, the traffic amount and the coefficient.
 2. (canceled) 3.The communication device according to claim 1, wherein the bandwidthallocation functioning unit; acquires the number of terminals to makeconcurrent transmission that indicates the number of slave unitsscheduled to transmit uplink transmission data in a next cycle ofbandwidth update, determines a coefficient by which the number ofterminals to make concurrent transmission is reflected in bandwidthallocation on the basis of the number of terminals to make concurrenttransmission, and determines a bandwidth to be allocated to the slaveunits on the basis of the queue length information, the traffic amountand the coefficient.
 4. The communication device according to claim 1,wherein the bandwidth allocation functioning unit; acquires the numberof active terminals corresponding to the number of active slave units,determines a coefficient by which the acquired number of activeterminals is reflected in bandwidth allocation based on the number ofactive terminals, and determines a bandwidth to be allocated to theslave units on the basis of the queue length information, the trafficamount and the coefficient.
 5. The communication device according toclaim 1, wherein the bandwidth allocation functioning unit updates thecoefficient for each cycle of bandwidth update, and determines abandwidth to be allocated to the slave unit using the updatedcoefficient.
 6. A communication system comprising: one or more than onefirst communication devices that operate as slave units; and a secondcommunication device as recited in claim 1, the second communicationdevice operating as a master unit.
 7. A method of allocating a bandwidthin a point-to-multipoint communication system in which slave units and amaster unit transmit and receive variable length data to and from eachother, the method being conducted by a communication device operating asthe master unit, the method comprising the steps of: acquiring queuelength information for extracting, from a receiving signal, queue lengthinformation scheduled to be transmitted from the slave units; measuringa traffic amount of uplink traffic of each of the slave units; andallocating a bandwidth for determining a bandwidth to be allocated tothe slave unit on the basis of the queue length information extracted inthe queue length information acquiring step, the traffic amount measuredin the traffic amount measuring step, and a bandwidth that can beallocated in one cycle of bandwidth update, and issuing a grantaccording to the determination, wherein the bandwidth allocating step isperiodically performed, and includes: a surplus bandwidth calculatingstep of calculating a necessary bandwidth of the slave unit on the basisof the queue length information and the traffic amount, and calculatinga surplus bandwidth by subtracting the necessary bandwidth from thebandwidth that can be allocated in one cycle of bandwidth update; acoefficient determining step of determining a coefficient by which thesurplus bandwidth is reflected in bandwidth allocation on the basis ofthe queue length information and the traffic amount; and a bandwidthdetermining step of determining a bandwidth to be allocated to the slaveunit on the basis of the queue length information, the traffic amountand the coefficient.
 8. (canceled)
 9. The method of allocating abandwidth according to claim 7, wherein the bandwidth allocating stepincludes: a transmission terminal number acquiring step of acquiring thenumber of terminals to make concurrent transmission that indicates thenumber of slave units scheduled to transmit uplink transmission data ina next cycle of bandwidth update; a coefficient determining step ofdetermining a coefficient by which the number of terminals to makeconcurrent transmission is reflected in bandwidth allocation on thebasis of the number of terminals to make concurrent transmission; and abandwidth determining step of determining a bandwidth to be allocated tothe slave unit on the basis of the queue length information, the trafficamount and the coefficient.
 10. The method of allocating a bandwidthaccording to claim 7, wherein the bandwidth allocating step includes: anactive terminal number acquiring step of acquiring the number of activeterminals corresponding to the number of active slave units; acoefficient determining step of determining a coefficient by which thenumber of active terminals is reflected in bandwidth allocation on thebasis of the number of active terminals; and a bandwidth determiningstep of determining a bandwidth to be allocated to the slave unit on thebasis of the queue length information, the traffic amount and thecoefficient.
 11. The method of bandwidth allocation according to claim7, wherein the coefficient determining step is performed for each cycleof bandwidth update, and the bandwidth determining step is performedusing the coefficient determined in the coefficient determining step.12. The communication device according to claim 3, wherein the bandwidthallocation functioning unit updates the coefficient for each cycle ofbandwidth update, and determines a bandwidth to be allocated to theslave unit using the updated coefficient.
 13. The communication deviceaccording to claim 4, wherein the bandwidth allocation functioning unitupdates the coefficient for each cycle of bandwidth update, anddetermines a bandwidth to be allocated to the slave unit using theupdated coefficient.
 14. The method of bandwidth allocation according toclaim 9, wherein the coefficient determining step is performed for eachcycle of bandwidth update, and the bandwidth determining step isperformed using the coefficient determined in the coefficientdetermining step.
 15. The method of bandwidth allocation according toclaim 10, wherein the coefficient determining step is performed for eachcycle of bandwidth update, and the bandwidth determining step isperformed using the coefficient determined in the coefficientdetermining step.